Device for producing microwave signals

ABSTRACT

The present invention describes a device for generating microwave signals, particularly for use in a distance and speed sensor in a motor vehicle. To this end, two laser sources are operated, whose emitted radiations are distinguished from each other by a set difference in wavelength. The two lasers are arranged in such a way that the emitted laser beams overlap spatially. A photodiode is disposed in this region in which the two laser beams interfere. From the superimposition product of the two laser beams, this photodiode generates an electrical output signal that has the differential frequency of the two superimposed laser beams. In this context, the frequency difference of the two lasers is selected so that the frequency of the generated microwave radiation lies in the range of the radar beam to be generated.

BACKGROUND INFORMATION

[0001] The present invention describes a device for generating microwave signals, particularly for use in a distance and speed sensor in a motor vehicle. To this end, two laser sources are operated, whose emitted radiations are distinguished from each other by a set difference in wavelength. The two lasers are arranged in such a way that the emitted laser beams superimpose spatially. A photodiode is disposed in this region in which the two laser beams interfere. From the superimposition product of the two laser beams, this photodiode generates an electrical output signal which has the beat frequency of the two superimposed laser beams. The difference in frequency between the two lasers is selected so that the frequency of the resulting beat lies in the range of the microwave signals.

BACKGROUND INFORMATION

[0002] From the publication “Optical Millimeter-Wave Systems for Broadband Mobile Communication, Devices and Techniques” by R.-P. Braun and G. Groβkopf, published at the “International Zürich Seminar of Broadband Communications-Accessing, Transmission, Networking” at the ETH Zürich in February 1998, it is known that microwave frequencies may be generated by the superimposition of optical waves of semiconductor lasers of different wavelength in a transmitter, modulated, and transmitted.

ESSENCE AND ADVANTAGES OF THE INVENTION

[0003] The essence of the present invention is to indicate a device for generating microwave signals, particularly for use in a motor vehicle.

[0004] An advantage of this device is that it has a compact design and, because of this, may be used in applications in which microwave signals are generated in the tightest space.

[0005] Moreover, it is advantageous that the microwave signals are generated with the aid of the emitted radiation of the two lasers that irradiate a photodiode in common.

[0006] The difference in the beat frequency generated by the two lasers advantageously lies in the range between 50 GHz and 100 GHz.

[0007] It is also advantageous that the two lasers are operated in an injection-locking operation, in that the radiation of a further or a plurality of further laser sources is injected into the two lasers.

[0008] It is particularly advantageous to monolithically integrate the laser sources, the photodiode, a high-frequency filter, the high-frequency amplifier, as well as other possible components on a single substrate.

[0009] The device is advantageously operated in a motor vehicle, particularly as a microwave generator for a distance and speed sensor.

[0010] Further features, uses and advantages of the present invention come to light from the following description of an exemplary embodiment of the invention which is shown in the FIGURE of the Drawing. In this context, all of the described or represented features, alone or in any combination, form the subject matter of the present invention, regardless of their combination in the claims or their antecedent, as well as regardless of their formulation and representation in the Specification and Drawing, respectively.

BRIEF DESCRIPTION OF THE DRAWING

[0011] In the following, an exemplary embodiment of the present invention is explained with reference to a Drawing, in which:

[0012]FIG. 1 shows a block diagram of a preferred specific embodiment.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0013]FIG. 1 shows a preferred exemplary embodiment of the device according to the present invention. Master laser 1 generates a frequency-stable output radiation. It is divided in a power splitter 2 into two sub-beams and supplied to two laser sources 3 and 4. The two laser sources 3, 4 are advantageously implemented in the form of two laser diodes. At this point, it should be pointed out that according to the invention, master laser 1 and power splitter 2 do not necessarily have to be present. If both laser sources 3, 4 emit a sufficiently frequency-stable output signal without master laser 1, then it is possible to dispense with master laser 1 and power splitter 2. In turn, these two laser sources 3, 4 each generate an output radiation 5 6. The frequencies of the two output radiation beams 5, 6 of laser sources 3, 4 differ by the amount that is to be generated at the output of photodiode 7 as the frequency of the microwave signal to be generated. For example, if the microwave signal to be generated is to have a frequency of 76 gigahertz, then the frequencies of output radiations 5, 6 of the two laser sources 3, 4 must differ by precisely this value, thus, by a frequency difference of 76 gigahertz, so that based on the mixing of the two beams 5, 6, which corresponds mathematically to a multiplication, because of the nonlinearity of photodiode 7, the desired microwave output frequency of 76 gigahertz results. These two radiation beams 5, 6 of the two laser sources 3, 4 are aligned spatially so that a region exists in which the two radiation beams 5, 6 intersect. In this region of the superimposition, a photodiode 7 is placed which is irradiated by both radiation beams 5, 6 simultaneously. To that end, the photodiode must be selected so that its band width permits detection of the differential frequency, but frequencies which are very much higher than the differential frequency can not be resolved. Because of the nonlinearity of photodiode 7, resulting from the superimposed, optical input signal is an electrical output signal having the desired microwave frequency which has the frequency difference of the two radiation beams 5, 6. The output signal of this photodiode 7 is conducted via a high-frequency filter 8, which may advantageously take the form of a band-pass filter. This filter 8 allows only the microwave signals to pass which lie in the output frequency band which is desired and is to be generated. Substantially higher or lower frequencies are filtered out of the input signal of filter 8. Finally, the microwave signal is amplified in a high-frequency amplifier 9 and fed to a further processing device 10. Further processing device 10 is advantageously a device for transmitting and receiving microwave radiation. According to the present invention, the described device made of electrical and optical components may also be produced on a single substrate as a monolithic semiconductor chip. Moreover, it is within the meaning of the device of the present invention that this device is mounted in a housing which is provided particularly for a speed and distance control in a motor vehicle, the device of the present invention being used as a frequency generator. 

what is claimed is:
 1. A device for generating microwave signals, made of at least two laser diodes (3, 4), a photodiode (7), a frequency filter (8) and a high-frequency amplifier (9).
 2. The device as recited in claim 1, wherein the emitted radiations (5, 6) of the two lasers (3, 4) irradiate a photodiode (7) in common.
 3. The device as recited in claim 1, wherein the two lasers (3, 4) emit radiation of different frequencies, and the frequency difference of the emitted radiation lies in the range between 50 GHz and 100 GHz.
 4. The device as recited in claim 1, wherein the emitted radiation of a further or a plurality of further laser sources (1) is injected into the two lasers (3, 4), the two lasers (3, 4) thereby being operated in an injection-locking operation.
 5. The device as recited in claim 1, wherein the device is operated in a motor vehicle, particularly as a microwave generator for a distance and speed sensor.
 6. The device as recited in claim 1, wherein the two laser diodes (3, 4), the photodiode (7), the high-frequency filter (8) as well as the high-frequency amplifier (9) are secured in a common housing, which in particular is the housing of a distance and speed sensor.
 7. The device as recited in claim 1, wherein the at least two laser diodes (3, 4), the photodiode (7), the frequency filter (8) as well as the high-frequency amplifier (9) are monolithically integrated on a single substrate. 